Defrostable refrigeration system



May 18, 1954 E. w. zEARFoss. JR

DEFROSTABLE REFRIGERATION SYSTEM I I /44 -2/b INVENTOR. [ll/[R If. Zf/MFfl/ZJ/I BY ciples.

Patented May 18, 1954 UNITED STATES ATENT OFFICE DEFROSTABLE REFRIGERATION SYSTEM Application February 28, 1951, Serial No. 213,204

This invention is concerned with refrigeration apparatus and, more particularly, relates to apparatus of the type having provision for heating the evaporator to effect removal of frost deposited upon the surfaces thereof. Broadly, the invention hasto do with improvements in heat pump defrosting systems of the type disclosed and claimed in the co-pending application of Malcolm G. Shoemaker, bearing Serial No. 189,183, filed October 9, 1950, issued March 17, 1953, as Patent No. 2,631,441, and assigned to the assignee of the present invention.

As is now well known, and as is set forth in the copending disclosure above-identified, periodic removal of accumulated frost is necessary in order to maintain the efficiency of a refrigeration machine the evaporator of which is operating at temperatures below the freezing point of water, and such defrosting has frequently been accomplished by shutting down the refrigeration system for a relatively extended period of time, during which the frost melts from the surfaces of the evaporator. Since extended discontinuities of operation of the system result in thawing of frozen foods contained within the evaporator, with resultant deterioration of such foods, and since the defrosting operation has frequently been troublesome and time-consuming, automatic and relatively frequent defrosting of the evaporator is desirable. such defrosting can be accomplished by subjecting the evap orator to a considerable quantity of heat over a relatively short period of time, and the most desirable and efficient modes of accomplishing this result have incorporated heat pump prin- As indicated above it is with improvements in this class of apparatus that the present invention is concerned.

More particularly it has been known to effect defrosting by by-passing the restrictor of the refrigeration system and delivering directly to the evaporator hot gaseous refrigerant flowing from the compressor, such refrigerant then condensing in the evaporator, with resultant absorption of latent heat and melting of accumulated frost. The refrigerant is then re-evaporated and re-circulated throughout the system, such cyclic operation being continued for a period of time sufficient to effect substantially complete removal of the frost which has accumulated.

In accordance with the teachings of the aboveidentified co-pending disclosure, such a defrosting cycle is accomplished through the agency of a valve disposed in the suction line and having connection with the discharge side of the com- 4 Claims. (Cl. 62-416) pressor. This valve is operable, through a suitable conduit, to by-pass the main capillary tube or restrictor and, concurrently, to establish flow of refrigerant from said discharge side of the compressor, through the suction line and thence through th evaporator in a direction reverse with respect to the normal direction of flow through said evaporator. A continuously open return passage or connection is so disposed in this type of system as to concluctunder defrosting conditions-condensed refrigerant flowing from what is normally the inlet side of said evaporator, directly back to the compressor. This refrigerant is in the liquid state, as aforesaid, and is returned to the gaseous state by any suitable heat exchange, and preferably by heat exchange taking place within the low pressure shell or dome of the compressor. The valve re quired in a system of this kind is not of the simplest type, and involves at least two movable valving parts.

While such a system has proven highly advantageous, I have recognized that there are further important advantages to be gained by simplifying the system and, specifically, by so modifying the system as to make it possible to eliminate one of the above-mentioned movable valving elements.

Accordingly, and with the foregoing in mind, it is the primary object of my invention to reduce the cost and complexity of a system of the type described briefly above, and to enhance its reliability in operation. In the achievement of this general objective I have devised a system in which a continuously open restricted connection is substituted for the stated portion of the valving, and by such substitution it is possible to include in the system only the simplest and most inexpensive valve structure including one movable and seated part.

Provision of apparatus which realizes the foregoing broad objectives, also makes it possible to achieve important collateral advantages. One of these is that the aforesaid passage which is utilized to return to the compressor refrigerant condensed in the evaporator, during the defrosting cycle, can be so disposed as to be surrounded by the insulation of the refrigerator cabinet. Insulation thereof is of substantial advantage since absorption of heat by the liquid regfrigerant flowing through said restricted passage would result in formation of, gas and consequent interference with unimpeded return of the condensed refrigerant to the compressor. Still further, the apparatus of this invention is characterized by the fact that it is possible to pass the flash gas which flows through the return line-during the normal refrigeration cycle-in heat exchange relation with the main capillary tube, thus increasing the efilciency of the normal cycle. It is also to be noted that the last-mentioned heat exchange relationship is further advantageous in that the liquid transmitted through the return passage, during the defrost cycle, is available to absorb heat from the suction line and the surrounding medium, thereby increasing the effectiveness of the defrosting apparatus by aiding in maintaining a relatively elevated. temperature at the compressor.

The manner in which the foregoing objects and advantages of my invention are achieved, will be fully understood from a consideration of the following description taken in conjunction with the accompanying drawings, in which:

Figure l is a diagrammatic representation of a refrigeration system including a preferred embodiment of the defrosting apparatus of the present invention; and,

Figure 2 is a diagrammatic illustration of a modified embodiment of the invention.

Now making detailed reference to the drawings, and initially to Figure 1 thereof, it will be seen that the preferred embodiment therein illustrated includes the elements of a refrigeration system of conventional type, namely, a compressor Ill, a condenser II, a continuously open restricted connection or capillary tube 52, an evaporator I3, and a suction line 14, a portion of the latter being disposed in heat exchange relation with the capillary tube I2, as shown at l5. Evaporator I3 is disposed in heat exchange relation with a compartment diagrammatically represented by the rectangle I 6, and which compartment is surrounded by the usual insulation shown fragmentarily at 11. Operation of the system is conventional, as respects the normal refrigeration cycle.

A return passage 18 has one end thereof connected in the circuit between said restrictor l2 and said evaporator 13, as by means of the flash gas separating chamber shown at l9, and has its other end connected to the suction line as shown at 20. This return passage, which is open under all conditions of operation, performs a useful function during the normal cycle in that the flash gas formed in the capillary tube or restrictor I2 is returned directly to the compressor through said passage, rather than reducing the effectiveness of the evaporator by passing therethrough. Separation of liquid and flash gas is, of course, effected by gravity within the small chamber E9. The passage I 8 is of moderately restrictive dimensions, presenting restriction which is less than the restriction of the capillary tube l2 and somewhat greater than the restriction presented by the evaporator circuit. This slight restriction insures that the liquid refrigerant flowing through the capillary tube will pass through the evaporator 13, rather than by-passing said evaporator and returning directly to the compressor through the passage iii.

In particular accordance with the present invention, the apparatus includes a by-pass conduit or connection 2! which is in communication with the discharge side of the compressor, by

reason of having one end thereof connected between the condenser and the capillary tube (see the connection at 22) and the other end thereof connected to the suction line, as at 23. A valve 24, which is preferably of the most simple soleq noid-actuated type, controls the flow of refrigerant through the by-pass conduit 2i and, when defrosting is required, the valve 24 is opened thereby modifying the normal flow of refrigerant within the system and establishing flow of hot gaseous refrigerant directly to the evaporator wherein the gaseous refrigerant is condensed, to effect the defrosting operation.

While, in the interest of simplicity in illustration and presentation of the invention, the control circuitry has been omitted from the drawing, it will be understood that the apparatus would be provided with a switch device effective to control the normal cycle, and with means for opening and closing the valve 24 to control the defrost cycle. Preferably, although not necessarily, operation of valve 24 may be under the control of a frost thickness switch device of the type described and claimed in applicants copending disclosure bearing Serial No. 183,757, filed September 9, 1950 and assigned to the assignee of the present invention.

When defrosting is required, and the solenoid valve '24 has been opened, warm gaseous refrigerant discharged by the compressor begins to flow through the conduit 2i into the evaporator (see the arrows applied to the drawing) and is condensed within the evaporator, as will now be understood.

To meet conditions which exist during the defrosting cycle, and to effect the above-mentioned simplification of the earlier apparatus referred to, thesystem of the present invention is featured by inclusion in the suction. line of a third or auxiliary restrictor25. This latter restrictor has less restriction than either. the return passage IE or the main capillary tube i2 and preferably comprises a short length of restricted tubing disposed in the suction line between the points 26 and 23 atwhich, respectively, the return passage [8 and the by-passconduit 2| have connection to the suction line l4. As indicated hereinafter in that portion of the description which has to do with the modified embodiment illustrated in Figure 2, the impedance presented by this auxiliary restrictor may be obtained in other ways than by use of the short section of restricted tubing illustrated in Figure 1.

Importantly, and by virtue of the presence of the restrictor 25, a considerable portion of the hot gaseous refrigerant flowing through the bypass conduit Zl toward and into the suction line I 4 is caused to flow through the path afforded by the evaporator i3, rather than icy-passin said evaporator and flowing directly back to the compressor through the suction line M, as would be the case if the restrictor 25 were not in the system, that is, if the suction line it were to present no appreciable impedance. As respects the refrigerant flowing through the conduit 21- toward the evaporator, it will be seen that the evaporator circuit including the return passage i8, and that portion of the suction line which includes the restrictor 25, are in parallel. Therefore it is evident that there will be a division of flow at the point 23, a portion of the hot gaseous refrigerant flowing through the evaporator to be condensed therein and returned to the compressor via passage i8 and the suction line 14. Another portion of the refrigerant will, of course, flow directly back to the compressor through the restrictor 25 and the suction line (4, and this latter portion is not effective in defrosting the coils of, the evaporator. Howeverithas compressor.

been found that the increase in suction pressure whichresults in thesystem of the present invention, when now of refrigerant is established through the conduit 2|, is so considerable that adequatedefrosting ofthe evaporator is accomplished with a rapidity consistent with the requirements imposed by the presence of frozen food in said evaporator. As will be understood, any given restriction will pass a great deal more refrigerant, by weight, in the liquid state, than it will pass in the gaseous state, and it has been found that when the defrost cycle has been established the effective impedance of the return passage i8 is relatively slight, since condensed refrigerant is flowing through said passage to the All of the refrigerant which flows through the by-pass conduit 2| and reaches the point 23 is in the gaseous state, and it will therefore be apparent that any refrigerant which returns directly to the compressor through the auxiliary restrictor 25 will be gaseous, whereas the refrigerant which flows out of the evaporator and through the return passage l8, during the defrosting cycle, is in the liquid state. Hence, as above set forth, a substantial part of the refrigerant flowing through the by-pass conduit 2| will pass into the evaporator for condensation therein, evenv though the physical restriction of the return passage I8 is greater than the physical restriction presented by the auxiliary restrictor Z5. Considered from another point of view, the fact that liquid refrigerant is passing through the return passage l8, whereas only gaseous reirigerant can traverse the auxiliary restrictor 25, results in the return passage presenting a smaller effective resistance to flow of refrigerant by weight.

In one representative embodiment of the invention the auxiliary restrictor comprised a section of tubing about two feet in length having the cabinet. Insulating the passage I8 is significant since it prevents formation of gas in said passage and consequent interference with return to the compressor of the refrigerant condensed in the evaporator during the defrosting operation. It is also to be emphasized that the invention is embodied in apparatus in which that flash gas which is taken off at the chamber !9, during the normal refrigeration cycle, is passed in heat exchange relation with the main capillary tube, as shown at l5. As indicated above, such heat exchange relation increases the efficiency of the normal cycle.

Evidently the degree of suction line restriction selected for use will vary with the design of the over-all machine and the operational requirements to be met. As shown in Figure 2, the preferred embodiment described just above is susceptible of considerable modification, as respects the suction line restriction and also with reference to the way in which the condensed refrigerant is caused to be returned to the compressor.

The modified form of apparatus shown in Figure 2 is generally similar to that which comprises the preferred embodiment, although said modified form includes several constructional differences of importance, which differences will now be set forth. The apparatus of Figure 2, in common with the preferred embodiment, also comprises the essential elements of a refrigerating system of known type, namely, a compressor, a condenser, a restrictor and an evaporator, shown at Illa, H a, I2a, and 13a, respectively, and also includes a suction line Ida, a portion of which is disposed in heat exchange relation with the capillary tube, as shown at Ma. In this second embodiment, however, the return passage [8a is arranged to deliver refrigerant directly back to the inlet side of the compressor, as shown at 26, rather than delivering such refrigerant to the suction line in the vicinity of the evaporator. Further. the by-passconduit 2 la delivers directly to the suction header 2! of the evaporator l3a, rather than leading to the suction line as is the case in the embodiment first described. However in both embodiments it will be noted that the by-pass conduit is in communication with the suction line, and it would therefore be possible for substantially all of the gaseous refrig erant to by-pass the evaporator and return directly to the compressor, if the apparatus did not include means for substantially reducing or preventing such return. In the embodiment of Figure 2 this requirement is again met by utilizing a suction line which presents appreciable restriction. In this form of the invention, however, the fiow impedance is provided by utilizing a suction line the entire length of which is of a somewhat reduced diameter as compared with the diameter of the suction line tubing employed in-the apparatus of Figure 1. In the interest of simplifying the machine, and in order to reduce the number of tubing connections, it may be desirable to resort to suction line restriction of the type utilized in the apparatus of Figure 2, rather than to utilize a short length of tubing of restricted diameter separately fabricated and disposed in the suction line.

The defrosting cycle of the modified apparatus illustrated in Figure 2 is, in all essential respects, similar to the operation of the preferred device, and it is therefore unnecessary to devote further description thereto.

From the foregoing description it will be understood that the present invention provides a heat pump defrosting system which is characterized by the highest degree of reliability in operation and by the elimination of relatively complicated and costly valve parts. While the foregoing description is limited to a consideration of two representative embodiments of the invention, it will be apparent that the invention is susceptible of a variety of changes and modifications without departing from the essential spirit of the invention. However, it will be recognized that those changes and modifications are contemplated, as may come within the scope of the appended claims.

I claim:

1. Defrostable refrigeration apparatus comprising. combination: a compressor; a condenser; a restrictor; an evaporator; conduit means including suction and feed lines so interconnecting said compressor, condenser, restrictor and evaporator in series flow circuit that refrigerant normally flows from the discharge side of said compressor through said condenser and said restrictor to the inlet side of said evaporator, the refrigerant thereafter returning from the suction side of 7 said evaporator to said compressor through said suction line; a valve-controlled conduit having one portion communicating with the discharge side of said compressor and another portion communicating with the suction side of said evaporator, said conduit by-passing said restrictor whereby, in response to opening of said valve, the aforesaid normal flow is modified and at least the major portion of the gaseous refrigerant delivered from the dischargeside of said compressor flows toward said evaporator through said conduit and without passing through said restrictor, at least a portion of said suction line and said evaporator comprising parallel refrigerant flow paths under the aforesaid modified condition of flow, and said suction line path presenting greater restriction to the flow of gaseous refrigerant than the path through the evaporator presents to the flow of condensed refrigerant, to insure that a substantial portion of the gaseous refrigerant flowing through said conduit passes into and through said evaporator for condensation therein; and means comprising a continuously open passage communicating with the said inlet side of said evaporator, said passage also communicating with the suction side of said compressor to provide for return to the compressor of refrigerant condensed within the evaporator under said modified condition of operation.

2. Refrigeration apparatus in accordance with claim 1, and further characterized in that the major portion of the restriction presented by'said suction line comprises a. tubing section disposed in the suction line adjacent the evaporator end thereof, said tubing section being of a diameter smaller than the diameter of other portions of said suction line.

3. Refrigeration apparatus in accordance with claim 2, and further characterized in that communication between said last-mentioned passage and the suction side of said compressor is provided by connection of said passage to said suction line between the mentioned tubing section and said compressor.

4. Refrigeration apparatus in accordance with claim 1, and further characterized in that portions of the apparatus including said evaporator are disposed within an insulated cabinet and at least the major portion of said last-mentioned passage is disposed within the insulation of said cabinet.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,530,440 Nussbaum Nov. 21, 1950 2,546,723 Clark Mar. 27, 1951 

